64-bit operating system has little effect on render speed (possibly can make it a very small bit slower, on the order of 1-3% from what I remember of Louguet's info).  Since Poser is currently only available in 32-bit versions, this is not a big benefit, but I've found it does improve memory usage problems.  On the other hand if you use other apps that ARE written in 64-bit instructions, you basically never have an app crash because it ran out of memory.  I have 8GB of memory, and I remember one instance in Cinema4D (64-bit) where I converted a complicated dynamic hair setup to polygons - many, many millions of polygons.  And then I rendered it.  The process took up 20gb of memory (RAM + virtual), but it did not crash.  A couple of times Windows complained that it needed to enlarge the swap file, but the render just went right on and eventually completed normally.  I was very impressed.

I use Windows XP Pro 64-bit edition and recommend it.  Some people are very happy with Vista 64, but while I have heard many complaints of application compatibility under Vista 64 I have heard virtually none about XP Pro 64.  All of my apps work VERY well.

I strongly recommend that you do not cut any corners on processor, motherboard, or video card, all three items are heavily used in 3D regardless of application.  I think an 8xxx series Nvidia card is the safest and fastest option for video.  Good luck!

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